The objective of these studies is to understand at the molecular level the interactions of myosin with itself, its isozymes, and other proteins necessary for the assembly of thick myofilaments and the organization of the myofilament lattice. This will be accomplished by biochemical, immunological and structural analysis of muscle mutants. The studies proposed focus on two problems in muscle development: first, to define the structural functions of myosin, and second, to explain the role of multiple myosins in those functions. The experimental plan is to exploit myofilament-lattice disrupted mutants of Caenorhabditis elegans, particularly those in the unc-54 gene, the structural gene for one of the myosin heavy chain polypeptides. Myosin from unc-54 mutants and the wild-type strain will be purified and its enzymatic and structural functions analyzed by: 1) affinity chromatography on ATP- and actin-Sepharose, 2) qualitative and quantitative analysis of its ability to polymerize to form dimers and filaments, 3) its ability to interact with paramyosin, and 4) its behavior in model muscle systems. Since the two body-wall muscle myosins can be separated, their individual properties in these assays will be compared. Further, I hope to develop techniques for mapping unc-54 mutations so that a fine structure-function map of myosin can be generated. C. elegans is uniquely suited for these studies as more than 50 unc-54 mutants are available for analysis and the myosin isoenzymes have been separated chromatographically, immunologically and genetically.